Trim Tab Drop Fins on R25 OB

[ID1890]

After reading Cruising Elvin Ray and other posts about drop fins, I decided to install Bennett Drop fins on on my 21 R25. Took the boat out today for the first time this season after install and I was very pleased with the results. Easier on plane, fuel economy increased, and smoother ride. Lenco Auto Glide worked fine with the drop fins. Worthwhile upgrade in my opinion.

 

[Almanac]

Did you need to recalibrate the autoglide after you installed them?

I know the setup process calibrates the pitch by starting with trim tabs up and deploying them 1 step every 6 seconds. If it saves the accelerometer/gyro position, then maybe it isn't needed, but if it ties that to the setting of how much tabs to deploy it may be necessary.

 

[ID1890]

I did not recalibrate, as everything worked as before. I will probably recalibrate next time we have a calm day to see if there is any additional improvement.

 

[TwoFootitis]

Hello ID1890,

I'm in the process of adding drop fins to my R23. The trim tabs are hard as hell. I've tried a few different bits and am having one heck of a time getting a hole punched through. What type of drill bits did you use? I do have a plasma cutter :shock: !

Thanks,

Doug

 

[CruisingElvinRay]

A fresh titanium bit, and cutting oil. Go slow. One bit got me through all 16 holes.


Sent from my iPhone using Tapatalk

 

[scross]

Second the use of sharp titanium, cobalt or carbide drill bit. Go slow, minimal pressure and don’t let it overheat. The tabs are stainless and it hardens as it gets hot. Heat is the enemy here.
There has been some past discussion about how to install drop fins. Bennett has not helped by giving conflicting information. The question is do you install the drop fins perpendicular to the trim tabs along the inside and outside edges of the tabs or do you install them parallel to the keel line?
If you install the drop fins perpendicular to the tabs it’s easy. If you install parallel to the keel it’s about an 8 degree offset from the trim tabs. At least that was the offset measured on the R-25 and R-27 Classics.
The benefit of installing parallel to the keel is less drag and reduced stress on the trim tabs themselves. At low speeds it’s probably not a big deal. At higher speeds the additional drag and stress might be a big deal.
On my R-25 Classic I installed them parallel to the keel based on emails from a Bennett manager. I will do the same when I install them on my 2017 C-28.

 

[ID1890]

Watch Cruising Elvin Ray's You Tube on trim tabs. Excellent step by step. I used DEWALT DWA1214 7/32" Pilot Point Industrial Cobalt Alloy Steel Drill Bit, drilled slowly with plenty of cutting oil. Bought 2, but only used 1.